Rear screen projection television displays have found great consumer interest due to a large image size. A primary disadvantage is the set volume and depth. For this reason manufacturers are always looking for ways to reduce size, for example by folding the optical path and also by making component parts smaller. This makes exact placement and alignment of the various components very important.
Light production is also very critical in projection displays. A projection lens, which generally comprises a number of optical elements such as individual lenses, generally projects the image to a viewing screen. A small misalignment of components in the projection lens, for example a misalignment of the light stop within the projection lens with respect to the optical axis of the projection lens, can cause a disadvantageous decrease in efficiency and a reduction in usable light for projecting the image. Such a misalignment can also of course introduce aberrations to the produced image.
Conventional projection lenses generally use an external lens stop or other separate light stop element within it to reduce glare and/or aberrations for example from non-desired portions of the image/light beam. This is fine for most projection lens applications, but in the most light-efficient projection display systems very small misalignments of the light stop can cause problems, and these very small misalignments of the light stop with respect to the other lenses of the projection lens can occur.
It is advantageous therefore to find ways to reduce the likelihood that the light stop used in a projection lens can get out of alignment.
Accordingly, in a first aspect of the invention, a projection lens includes at least one optical lens element and a non-radially symmetrical light stop applied directly to a surface of the optical lens element.
In a second aspect of the invention, a projection display system includes a light engine, a projection lens disposed to receive an image, and a projection screen disposed to receive the image.
In a third aspect of the invention, a method for aberration selectively blocking light in a projection display system includes projecting an image through a projection lens that includes an optical lens element and applying a non-radially symmetrical light stop directly to a surface of the optical lens element.